1. Field of the Invention
This invention relates in general to certain new and useful inprovements in lamp switching circuit devices and method and more particularly to a lamp switching circuit device and method which sequentially energizes one or more lamps in a circuit arrangement without impairing the efficiency of operation of any of the lamps when operating.
2. Brief Description of the Prior Art
In many cases, conventional fluorsecent light fixtures are constructed so as to physically retain and energize a pair of phosphor excitable lamps, such as fluorescent lamps. The ballast and circuitry in these fixtures are typically designed so that the two lamps in the fixture are essentially electrically 180 degrees out of phase. This arrangement is used in order to cancel out visible flicker to some extent. Thus, two lights in a fixture or otherwise lights in pairs are employed to reduce the noticeable effects of flicker, even though the extra lumen output of two lamps in not necessarily required.
In many cases, it has been found in office buildings and other commercial installations, that it is possible to eliminate one or more lamps of the fixture without appreciably reducing total light output so that inefficiency and eye fatigue do not result. In other words, many commercially available fixtures were constructed so that an excess of light was generated for a given purpose.
In recent years, and due to at least in part to severe shortages in available energy, and particularly electrical energy, and also due to the high cost of electrical energy, there has been an interest in reducing the available light output in order to reduce the total cost of operation. However, in many of the commercially available fluorescent lamp fixtures, the removal of one of the lamps, particularly in a series connected circuit of the lamps, resulted in a very substantial inefficiency of operation. If the remaining lamp was able to operate at all, depending upon the circuit configuration, then there was a resultant inefficiency in that the remaining lamp produced less light output for a given level of power consumption or otherwise the ballast in the electrical circuit which operated the lamp operated inefficiently thereby decreasing operating life.
In order to obviate these problems, there has been some use of the so-called "phantom tube", that is, a lamp tube which is similar in appearance and size to a conventional fluorsecent lamp but which does not generate any lumen output and similarly, does not utilize any electrical power, as such. Lamps of this circuit arrangement to compensate for the missing lamp. Lamps type utilize an interior capacitor which is introduced in the of this type are described in U.S. Pat. No. 3,956,665 to Westphal and U.S. Pat. No. 4,255,692 to David E. Burgess. Other lamp substitute devices are also shown in U.S. Pat. No. 4,348,614 to David E. Burgess.
The devices of the aforementioned type were oftentimes ineffective, if not undesirable. Due to the fact that only one of the lamps in the circuit was operating, and moreover, due to the fact that this lamp had to accept any increased load factor as a result of one lamp missing, the overall life span of the remaining lamp was materially reduced. In large institutions where numerous fluorsecent lamps are employed, this necessitated frequent changing of the lamps which materially increased the overall maintenance cost of the light systems.
There have been other proposed arrangements for reducing the amount of light in an attempt to reduce the energy consumption and cost of light operation. For example, fixed static dimmers were introduced to work in conjunction with the ballast circuit for reducing power consumption and light output in applications where the reduced light was acceptable. Further, more sophisticated controllers were also designed and which utilized microprocessor control for turning light systems on and off based on work shedules within a facility. Other controllers were designed to provide minimal light by distinguishing all but a very few of the lights within a circuit.
In an attempt to also increase the light output from a light fixture while de-energizing one of the lamps therein, there have been attempts to use highly reflective metal and plastic surfaces on portions of the fixtures for reflecting the light from the remaining lamps which operate. These reflectors are formed with a contour so as to amplify the light from the fixture and direct it into a usable surface area in an optimum manner. These reflective surfaces are also effective in that they enhance the reflective characteristics within and around the fluorsecent lamps, whether or not operating, so that it appears that all lamps in a fixture are operating when only certain of the lamps may, in fact, be generating the light output.
One of the principal problems which has been encountered in the prior art by de-energizing some of the lamps and maintaining the energization of other of the lamps is the reduced life span of the lamps which are operating. As an example, the practicality of maintaining a four lamp, two ballast fluorescent fixture requires that all lamps must be replaced in about an every three year period because they will have utilized their effective 12,000 to 20,000 hours of expected operating life. If any one of the lamps in that ballast are removed or de-energized, the maintenance time may increase somewhat. Nevertheless, even if the maintenance time does not increase, when one lamp in a two lamp ballast burns out, there is an urgency introduced into the maintenance.
There is needed a switching circuit which will effectively and sequentially energize only certain of the lamps in a lighting fixture and sequentially thereafter energize the other of the lamps in the fixture when power is interrupted and reapplied. In this way, optimum use of the lamps is obtained and optimum maintenance schedules are achieved.